The present invention relates generally to digital audio/video program and transport stream demultiplexing. More particularly, this invention relates to a system and method for using sequencing information found within a local header to permit the proper synchronization of packets to a plurality of subsidiary interfaces within the post-processing environment of an MPEG-2 packet demultiplexing architecture.
The development of digital video technology has made possible a variety of telecommunication applications, including video conferencing, video telephony, high-definition television (HDTV), and motion pictures at our desktops to name but a few. The multi-media explosion, including still pictures, moving video, and audio, is already proliferating the threads of the World Wide Web. Technological advances in digital video are presenting new opportunities as well, such as for existing quality television distribution, interactive television, and movies and news on demand.
In order to reduce the high cost of video compression codecs and resolve manufacturer equipment interoperability issues, standardization of digital video techniques has been a high priority. Furthermore, as the computer, telecommunications, and consumer electronics industries continue to amalgamate, the need for standardization becomes more prevalent. To address these and other issues, the International Organization for Standardization (ISO) has undertaken efforts to provide standards for various multimedia technologies, including digital video and audio. The expert group of the ISO that has undertaken this obligation is the Moving Picture Experts Group (MPEG). While the MPEG-1 standards addressed many of the issues facing digital video transmission today, they were not suited for broadcast environments or television applications. Therefore, the ISO developed the MPEG-2 standard (ISO/IEC 13818) to respond to these needs.
The MPEG-2 standard does not, however, define each part of the digital link. This allows for expansion and enhancement of the market via the technology industry. For example, while the MPEG-2 defines a format that can be used to describe a coded video bitstream, it does not specify the encoding method. Instead, it defines only the resulting bit stream.
The MPEG-2 standard is often associated with the video compression aspect of digital video. While video compression is an important part of the MPEG standards, MPEG-2 includes a family of standards involving different aspects of digital video and audio transmission and representation. The general MPEG-2 standard is currently divided into eight parts, including systems, video, audio, compliance, software simulation, digital storage media, real-time interface for system decoders, and DSM reference script format.
The video portion of the MPEG-2 standard (ISO/IEC 13818-2) sets forth the manner in which pictures and frames are defined, how video data is compressed, various syntax elements, the video decoding process, and other information related to the format of a coded video bitstream. The audio portion of the MPEG-2 standard (ISO/IEC 13818-3) similarly describes the audio compression and coding techniques utilized in MPEG-2. The video and audio portions of the MPEG-2 standard therefore define the format with which audio or video information is represented.
Another important part of the MPEG-2 standard is the MPEG-2 Systems portion (ISO/IEC 13818-1). At some point, the video, audio, and other digital information must be multiplexed together to provide encoded bitstreams for delivery to the target destination. The Systems portion of the standard defines how these bitstreams are synchronized and multiplexed together. Typically, video and audio data are encoded at respective video and audio encoders, and the resulting encoded video and audio data is input to an MPEG-2 Systems encoder/multiplexer. This Systems multiplexer can also receive other inputs, such as control and management information, private data bitstreams, and time stamp information. The resulting coded, multiplexed signal is referred to as the MPEG-2 transport stream. More specifically, it is referred to as the transport stream where the digital information is delivered via a network to be displayed in real time, and is referred to as a program stream where a local media-based system is used (e.g., CD-ROM, local hard disk, etc.).
The video and audio encoders provide encoded information to the Systems multiplexer and provide this information in the form of an xe2x80x9celementary streamxe2x80x9d. The encoded output of a video encoder provides a video elementary stream, and the encoded output of an audio encoder provides an audio elementary stream. In each of these cases, the elementary stream can be organized into xe2x80x9caccess unitsxe2x80x9d, which can represent a picture or an audio frame depending on whether it is part of the video or audio elementary stream. These elementary streams are xe2x80x9cpacketizedxe2x80x9d into packetized elementary streams (PES) which are comprised of many PES packets. Each PES packet is size-variable, and includes a packet payload corresponding to the data to be sent within the packet, and a PES packet header that includes information relating to the type, size, and other characteristics of the packet payload. The PES packet payloads are not fixed-length, which allows the packet payload to correspond to the access unit of its particular elementary stream.
PES packets from the video and audio encoders are mapped into transport stream packets (TSP) at the Systems encoder/multiplexor. Each TSP includes a payload portion which corresponds to a fixed-length portion of the PES packet stream, and further includes a TSP header. The transport stream packet header provides information used to transport and deliver the information stream, as compared to the PES packet header that provides information directly related to the elementary stream. Although one PES packet may occupy multiple transport packets, byte xe2x80x9cstuffingxe2x80x9d is used to fill the remainder of a transport packet payload which was not completely filled by a PES packet, thereby allowing each PES header to be positioned at the beginning of the transport packet payload. This allows the PES header to be more easily synchronized at the decoder.
The consecutive flow of transport stream packets form the MPEG transport stream. MPEG-2 Systems provide for two types of transport streams. The first is the single program transport stream (SPTS), which contain different PES streams, but share a common time base. The multi-program transport stream (MPTS) is a multiplex of various single program transport streams, which in turn may be multiplexed into various network channels for multi-channel delivery to the media user.
The challenge then becomes determining an efficient manner to extract the desired information from the program or transport stream for decoding at the video, audio, or other decoders. Before the transport stream is decoded, the transport packets must undergo analysis, synchronization, demultiplexing, as well as other packet manipulating functions. These functions can be managed by devices such as a MPEG transport demultiplexor, and must be managed properly to execute the functions in the most efficient manner possible to enhance packet transport speed and ease. Due to the extraordinarily high data transfer requirements associated with motion video, packet throughput time is a paramount concern.
One problem affecting the efficiency of such transport demultiplexors is the potentially inefficient use of processor time in synchronizing packets received into the proper sequence to account for various transport delays for individual packets. Prior art systems have utilized the processor to individually determine where each elementary stream should be stored prior to being sent to their respective decoders. This, however, can reduce the amount of time that the processor can be used for other processing tasks. Furthermore, the processor may need to obtain information from within the system in order to create the sequencing information, which can further reduce processor capacity and affect system speed.
Accordingly, there is a need for a system and method for use of sequencing information in a local header that allows proper synchronization of packets to subsidiary interfaces within the post-processing environment of an MPEG-2 packet demultiplexing architecture. The present invention therefore offers advantages and provides solutions to shortcomings of the prior art.
The present invention is directed to a system and method for demultiplexing and distributing transport packets, such as MPEG-2 transport packets, by generating and associating a locally-generated header with each of the transport packets to create a self-contained modified packet which incorporates essential distribution information therein.
In accordance with one embodiment of the invention, a method for enhancing transport packet demultiplexing and distribution in a digital transport demultiplexing system that inputs a stream of digital multimedia transport packets is provided. Each of the transport packets includes a packet identifier (PID) to identify the digital program or elementary stream to which it corresponds. Local packet information is generated for each of the transport packets, which is used in identifying and distributing the transport packets. A local header is created that includes the generated local packet information, and the local header is linked to its corresponding transport packet to create a modified transport packet. In this manner, each of the modified transport packets represents a self-contained digital transport packet having local distribution information contained therein.
In accordance with another aspect of the invention, a transport stream demultiplexing apparatus for use in a digital transmission system capable of providing a plurality of digital transport packets to a digital program presentation device is provided. Each of the digital transport packets includes a serial isochronous interface field and a transport sequence field. The serial isochronous interface field is used by the system to determine if the individual data packet is to be transmitted onto an output link having an isochronous data stream. The transport sequence field contains information necessary to output the data packet into the isochronous data stream with a delay necessary to maintain the data packets synchronization with the other data packets within the isochronous data stream.
The above summary of the present invention is not intended to describe each illustrated embodiment or implementation of the present invention. This is the purpose of the figures and the associated discussion which follows.